The invention relates to optical transmission systems and more particularly to the power level of optical signals transmitted over an optical line/fiber.
In low powered optical transmission systems, optical signals are transmitted over an optical line/fiber at a so-called class 1 power level (which is typically less than 10 dBm for an optical wavelength of 1550 nm). If the line were accidentally cut, it is likely that the optical signal would still be transmitted, and thus emitted from the transmission side of the cut fiber. A receiver at the opposite end of the other side of the cut fiber would detect loss of the transmitted signal and issue an alarm, which would cause a craftsperson to be dispatched to the location at which the fiber is cut to repair the cut in a conventional manner. It is unlikely that, due to the low power of the transmitted light signal, the craftsperson would be harmed if he/she happened to look at the concentrated light signal being emitted from the transmission end of the cut fiber while making the repair. If, however, the system were a high power system, one which transmits optical signals at a class 3B power level (which is typically greater than 17 dBm for an optical wavelength of 1550 nm), then it is likely that the craftsperson would be harmed as a result of looking at the concentrated/focused light. (Note that such harm could include damage to the craftsperson""s retina.) Moreover, system apparatus may be harmed from a power surge as the system cable is restored to service.
To avoid such harm, there is need for a high power optical transmission system that automatically reduces the power of a light signal that is being transmitted over a fiber that appears to be cut at some upstream point. In fact, this need is mandated by the well-known international standard IEC 825 for optical transmission systems as set forth by International Electro-technical Commission (IEC), see, for example, the IEC publication International Standard IEC825, Safety of Laser Products part 1: Equipment Classification, Requirements and User""s Guide, 1993, which is hereby incorporated by reference.
We deal with the foregoing problem by automatically reducing to safe level the high power level at which an optical amplifier is transmitting an optical signal over a fiber/path that may be cut.
More specifically, we arrange a controller associated with an optical node that detects the loss of signal (LOS) on a fiber so that it sends to an upstream controller a message requesting that the optical amplifier transmitter connected to the fiber associated with the LOS reduce its power amplification at which it is transmitting optical signals over that fiber, an upstream element receiving the message then causes the optical amplifier to reduce the power level at which it is transmitting optical signals from a first power level to a second power level.
These and other aspects of our invention are set forth in the following detailed description and accompanying claims and drawings.